1. Field of the Invention
The present invention relates to a bioreactor including one or more features that improve bioreactor liquid infiltration and gas recovery. The bioreactor of this invention described creates an extremely large area for infiltration and gas recovery. It further eliminates the vertical gas wells and replaces them, in part, with self draining angular wells in the infiltration area. The surface area for gas recovery based on the porous media supplied is an order of magnitude greater than the vertical well based gas recovery systems.
2. Description of the Art
About 15 years ago, landfill owners began using leachate recirculation as a remediation method. The dominant techniques have been to inject leachate into landfills using horizontal leachate piping, vertical wells, or applying leachate to the working landfill face surface. Distribution of the liquid over a large area has always been concern. Often landfill material surrounding the leachate injection sites become clogged with slime, fines or calcium/iron complexes. Additionally, the gas recovery wells, that are typically vertical, often filled with water and or leachate. These flooded wells resulted in poor gas collection and the need to place expensive liquid pumps in the gas well casings.
Differential landfill settlement complicates compliance with the environmental regulations related to gas and simultaneously increases maintenance costs dramatically. Since the 1980s' over 90% of the landfill gas recovery systems in the United States and Canada use vertical gas extraction wells. Standard practice is to drill a 30″ to 36″ diameter well and insert a 6″ to 8″ diameter gas pipe and then fill the boring with stone. This system was designed for landfills that do not apply large volumes of liquid, such as leachate, to landfills. Over the years with the development of leachate recirculation, air operated pumps have become standard in wet landfills. This has resulted in a high maintenance costs. Along with these pumps, many landfills are increasing the density of the gas recovery wells.
Advances in landfill remediation have been made recently. U.S. Pat. No. 6,742,962 discloses a horizontal infiltration and gas recovery system. The system is designed to eliminate some of these problems with gas recovery in wet landfill systems. While the system is an improvement over vertical gas recovery systems it still requires liquid pumps associated with the gas recovery wells and the system is subject to oxygen intrusion if the cover soil is not properly compacted. Another issue with this system is the potential for limited liquid coverage due to non-homogeneous waste placement and chemical blinding of the trenches. U.S. Pat. No. 6,283,676 discloses systems that employ short-term compressed air addition into a landfill in order to initiate aerobic bacterial growth and degradation.
Despite these advances, there remain problems with existing leachate recirculation and/or landfill gas recovery systems including (1) the continued dependency on vertical gas wells; (2) The requirement to pump liquids out of vertical gas wells as the infiltration field became saturated; (3) historically, infiltration systems do not allow for surface application initially followed by deep infiltration and the landfill is filled for the apparatus is covered; (4) the need for a system that would allow for infiltration and gas recovery simultaneously. Furthermore, there is a need to be able to drain liquids from the gas collection system and improve gas recovery for the saturated infiltration field. Additionally gas systems in older wet landfills are prone to maintenance issues related to settling of the gas system. Vertical wells sheer off and crush and the interconnecting horizontal gas headers often water out.